This invention relates to a hybrid or compound antenna unit and, in particular, to a hybrid antenna unit for mounting a plurality of different antennas therein.
In the manner which is known in the art, recently, various different antennas are mounted in a vehicle such as an automobile. For example, there are, as such antennas, a GPS (Global Positioning System) antenna, an SDARS (Satellite Digital Audio Radio Service) antenna, a cellular phone antenna, an AM/FM radio antenna, or the like.
The GPS (Global Positioning System) is a satellite positioning system using artificial satellites which are called GPS satellites. The GPS is a system which receives radio waves (GPS signals) from four GPS satellites among twenty-four GPS satellites orbiting the Earth, measures, on the basis of the received waves, a position relationship and a time error between a mobile object and the four GPS satellites, and accurately calculates, on the basis of a principal of triangulation techniques, a position and/or a height of the mobile object on a map.
In recent years, the GPS is used in a car navigation system for detecting a position of a running automobile or the like and becomes widespread. In the car navigation system, a car navigation apparatus comprises a GPS antenna for receiving the GPS signals, a processing unit for processing the GPS signal received by the GPS antenna to detect a current position of the vehicle, a display unit for displaying, on the map, the position detected by the processing unit, and so on. A plane antenna such as a patch antenna is used as the GPS antenna.
On the other hand, the SDARS (Satellite Digital Audio Radio Service) is a radio service according to a digital radio broadcasting using artificial satellites (which will called “SDARS satellites” hereinafter) in the United States of America. That is, in recent years, a digital radio receiver, which receives the satellite wave from the SDARS satellites or the terrestrial wave so as to listen to the digital radio broadcasting, has been developed and is put to practical use in the United States of America. Specifically, two broadcasting stations called XM and Sirius provide radio programs on 250 or more channels in total. The digital radio receiver is generally mounted on a mobile object such as an automobile and is adapted to receive a radio wave having a frequency of about 2.3 gigahertz (GHz) as a received wave to listen to the digital radio broadcasting. In other words, the digital radio receiver is a radio receiver capable of listening to mobile broadcasting. Inasmuch as the received wave has the frequency of about 2.3 GHz, a reception wavelength (resonance frequency) A thereof is equal to about 128.3 mm. It is noted here that the terrestrial wave is a radio wave obtained by receiving the satellite wave at a ground station, slightly shifting the frequency of the satellite wave, and retransmitting the linear polarized wave. Thus, the terrestrial wave is the linear polarized wave exhibiting linear polarization while the satellite wave is a circular polarized wave exhibiting circular polarization. A plane antenna such as a patch antenna is used as the SDARS antenna.
An XM satellite radio antenna apparatus normally serves to receive circular polarized radio waves from two stationary satellites and, in an insensitive zone of the circular polarized waves, receives a radio wave by using a terrestrial linear polarization portion of the radio antenna apparatus. On the other hand, a Sirius satellite radio antenna apparatus normally serves to receive circular polarized radio waves from three orbiting satellites (synchronous type) and, in the insensitive zone, receives a radio wave by a terrestrial linear polarization portion of the radio antenna apparatus.
As described above, the radio wave having the frequency of about 2.3 GHz is used in the digital radio broadcasting. Therefore, an antenna for receiving the radio wave must be located outside as known in the art. If the digital radio receiver is mounted in the mobile object such as the automobile, the antenna unit is often attached to a roof of the mobile object (car body).
A hybrid antenna unit is disclosed in U.S. Patent Application Publication No. US 2006/0290580 A1 which will be called a first patent document. The hybrid antenna unit disclosed in the first patent document comprises a main circuit board having first and second surfaces opposite to each other, a first antenna unit, mounted on the first surface, for receiving a first radio wave from a first kind of artificial satellites, and a second antenna unit, mounted on the first surface, for receiving a second radio wave from a second kind of artificial satellites. The first antenna unit comprises the GPS antenna for receiving the first radio wave from the GPS satellites as the first kind of artificial satellites. The second antenna unit comprises the SDARS antenna for receiving the second radio wave from the SDARS satellites as the second kind of artificial satellites.
At any rate, the hybrid antenna unit disclosed in the first patent document comprises a first plane antenna used as the GPS antenna and a second plane antenna used as the SDARS antenna which are put side by side with each other. In addition, the hybrid antenna unit disclosed in the first patent document further comprises an antenna element and an antenna case in which the antenna element is inserted. The main circuit board is mounted in the antenna case. The antenna element comprises a first pole antenna element and a second pole antenna element The first pole antenna element is for receiving a radio wave of AM/FM radio bands while the second pole antenna element is for receiving and transmitting a radio wave for a cellular phone (e.g., a mobile telephone or a car telephone). That is, the second pole antenna is a cellular antenna. On the second surface of the main circuit board, a booster circuit for the first pole antenna element is mounted.
The hybrid antenna unit disclosed in the first patent document comprises two antenna units which put side by side with each other. The hybrid antenna unit is therefore disadvantageous in that it is upsized.
An antenna element is disclosed in U.S. Patent Application Publication No. US 2009/0002229 A1 which will be called a second patent document. The antenna element disclosed in the second patent document can receive a GPS signal and a SDARS signal as two kinds of electric waves. The antenna element comprises a dielectric board, a first antenna radiation electrode formed on a top surface of the dielectric board at an outer region, a second antenna radiation electrode formed on the top surface of the dielectric board at a central portion, a ground electrode formed on a bottom surface of the dielectric board, a feeding pattern formed on the side surface of the dielectric board for feeding to the first antenna radiation electrode by electromagnetic coupling, and a feeding pin having an end connected to the second antenna radiation electrode. A combination of the first antenna radiation electrode, the ground electrode, and the feeding pattern serves as a first antenna portion for receiving a first radio wave. A combination of the second antenna radiation electrode, the ground electrode, and the feeding pin serves as a second antenna portion for receiving a second radio wave.
The second patent document further comprises a hybrid antenna unit comprising the antenna element and a bar antenna. The bar antenna receives both of a radio wave of AM/FM radio bands and a radio wave for a mobile telephone or a car phone. The antenna element is mounted on a circuit board. The circuit board comprises a first processing circuit for processing the first radio wave to produce a first processed signal, a second processing circuit for processing the second radio wave to produce a second processed signal, and a combining circuit for combining the first processed signal with the second processed signal to produce a combined signal. A combination of the antenna element and the circuit board serves as an antenna unit. The antenna unit is covered by an antenna base and a top case. The bar antenna stands on the top case in a slanting position.
A composite antenna module is disclosed in Japanese Unexamined Patent Publication No. 2001-267843, namely, JP-A-2001-267843 which will be called a third patent document. The composite antenna module disclosed in the third patent document comprises a circuit board having an upper surface and a rear surface opposite to each other, a plurality of types of antennas arranged on the upper surface of the circuit board, and a circuit including a signal combining circuit part formed on the rear surface of the circuit board. The signal combining circuit part forms a combined signal of high frequency signals of the various antennas. The various antennas are for S-DAB, for VICS, for GPS, and for remote keyless entry.
A composite antenna device is disclosed in Japanese Unexamined Patent Publication No. 2007-013293, namely, JP-A-2007-013293 which will be called a fourth patent document. The composite antenna device disclosed in the fourth patent document comprises a board having a principal side and a rear side opposite to each other, a feeding electrode, a planar antenna element, an electric circuit, and a pole antenna element. The principal side of the board is connected to ground except its prescribed region (installation base). The feeding electrode is formed to the prescribed region. The planer antenna element is mounted to the principal side of the board. The electric circuit is connected to the planer antenna element and is mounted to the rear side of the board. The pole antenna element stands upright from the feeding electrode apart from the planar antenna element on the principal side of the board. The pole antenna element includes a coil part wound in a form of a coil. The planar antenna element comprises a patch antenna and for GPS. The pole antenna element is for wireless LAN.